Aviation buff John Zimmerman was at a weekly gathering of neighbors Friday night when he noticed something peculiar: a small plane circling a route overhead that didn’t make sense to him.

It was dark, so a sightseeing flight didn’t make sense, and when Zimmerman pulled up more information on an aviation phone app he routinely checks, he had immediate concerns.

The plane’s flight path, recorded by the website flightradar24.com, would eventually show that it circled downtown Minneapolis, the Mall of America and Southdale Center at low altitude for hours starting at 10:30 p.m., slipping off radar just after 3 a.m.

“I thought, ‘Holy crap,’ ” said Zimmerman.

Bearing the call sign N361DB, the plane is one of three Cessna 182T Skylanes registered to LCB Leasing of Bristow, Va., according to FAA records. The Virginia secretary of state has no record of an LCB Leasing. Virtually no other information could be learned about the company.

Zimmerman’s curiosity might have ended there if it weren’t for something he heard from his aviation network recently: A plane registered to NG Research — also located in Bristow — that circled Baltimore for hours after recent violent protests there was in fact an FBI plane that’s part of a widespread but little known surveillance program, according to a report by the Washington Post.

Similar flights have since been spotted near Chicago, Boston and in California, according to the American Civil Liberties Union. The ACLU has filed several Freedom of Information Act requests for more information.

It believes the planes use cameras and infrared imaging technology to photograph people and vehicles in a broad swath of the city; technology to sweep up cellphone data from a plane also exists, but it’s not clear if the FBI flights use it.

A spokesman for the Twin Cities FBI office had no comment on the recent flight, saying he couldn’t speak to an “operational matter.” He declined to say if the plane belongs to the FBI or if it was acting at the request of a local law enforcement agency.

However, the FBI acknowledged its role in the earlier Baltimore flights. The agency issued a statement saying the flights “were not there to monitor lawfully protected first amendment activity, and any FBI aviation support to a local law enforcement agency must receive high-level approvals.”

The Minneapolis Police Department, the Bloomington Police Department and the Hennepin County Sheriff’s Office said they had no knowledge of the flight. Flying Cloud Airport in Eden Prairie couldn’t confirm past flights, but the same plane was confirmed over the Twin Cities on Thursday.

A similar flight — nighttime, circling at low altitude — in a suburb of Boston after the 2013 marathon bombing generated media coverage and concern among ordinary citizens about the “Quincy mystery plane.” That Cessna 182 Skylane also was traced to Bristow, Va., and registered to a company called RKT Productions, according to news reports and witnesses. It was later reported by the Quincy Patriot Ledger that the plane was tracking Khairullozhon Matanov, a Quincy resident who earlier this year pleaded guilty to obstructing the bombing investigation.

Bristow, just outside Washington, D.C.’s Beltway, has 65 planes registered there, the bulk of them small Cessna 182s registered to a handful of companies with two- or three-letter acronyms in their names, like LCB Leasing.

Zimmerman, who spotted the plane over Bloomington, said he pored through FAA records to find the call letters for each plane and then searched for images of them. He found photographs that show the planes outfitted with “external pods” that could house imagery equipment. He also found some of the planes modified with noise-muffling capability. That’s not common for a small plane, he said.

“The fact is there are several very powerful surveillance technologies that are deployed by fixed-wing aircraft circling over cities,” said Jay Stanley, a senior policy analyst with the ACLU. “These are powerful surveillance technologies that we think the public ought to have a role in discussing and debating.”

The planes use “persistent wide-area surveillance” to photograph large areas for hours at a time, Stanley said. The captured images allow authorities to go back in time, if necessary, to trace pedestrians and vehicles who come to their attention.

Other devices known as “dirtboxes,” “Stingrays” or “IMSI catchers” can capture cellphone data. Stanley said it’s still unclear what technologies have been used in the surveillance flights.

Zimmerman said he’s in favor of using technology to fight crime but criticized the government’s secretive approach, the same criticism that was leveled in Boston when a city made skittish by the marathon bombing had to wonder why planes were flying low overhead at night.

“Why don’t we just say these are official things, rather than clouding them in three-letter contract companies?” Zimmerman asked. “I would feel better if these guys just flew the colors. I think we would all be better off.”